1. Field of the Invention
The present invention relates to internal combustion engines and, more particularly, to a fuel and air mixture injection port for an internal combustion engine.
2. Brief Description of Prior Developments
Small two-stroke engines have many desirable characteristics including: simplicity of construction, low cost of manufacturing, high power-to-weight ratios, high speed operational capability and, in many parts of the world, ease of maintenance with simple facilities. U.S. Pat. No. 5,503,119 discloses a crankcase scavenged two-stroke engine wherein fuel is deposited in a transfer passage between the crankcase and a combustion chamber of the cylinder. Deere and Company manufactures and sells a new type of small two-stroke engine which uses an accumulator to deliver fuel directly into a combustion chamber of the engine. Because a majority of the fuel is not passed through the crankcase of the engine before it enters the combustion chamber, delivery of the fuel to the combustion chamber can be relatively precisely controlled to minimize production of pollutants by having a much more complete burn in the combustion chamber.
One problem that can arise in this type of new relatively precise fuel delivery system is that, at a cold starting condition, the engine can exhibit a very lean running behavior. The engine can suffer from poor warm-up characteristics presented in a bucking (severe misfiring) behavior during warm-up while the carburetor is set at a part-choke position, and thus require a prolonged warm-up time. The bucking behavior of the engine during warm-up is a result of what would be described as a very lean air/fuel mixture.
The air/fuel mixture during cold start appears to be well above the stocichiometric level. This is not due to either a failure in the carburetor delivery system or a failure in the engine induction behavior. The induction passage provides a wide path for the fuel to be injected upward into the combustion chamber. Poor atomization of the fuel can result in large droplet sizes; which are more difficult to burn. Thus, when the engine is cold, a smaller percentage of the fuel delivered is burnt with the available air resulting in what appears to be a lean engine. As the engine warms up, fuel vaporizes resulting in smaller droplet sizes. The air/fuel mixture with the smaller droplet sizes begins to approach the proper level.
There is a desire to refine the injector design to improve fuel atomization under all conditions; especially a cold start condition. The engine could die on the non-choke position if not properly warmed-up on the part-choke position. The warm-up period could be well over a minute in most cases. That characteristic is very undesirable by consumers since it could incorrectly reflect a poor quality engine. There is a desire to eliminate this type of behavior. There is a desire for a new type of fuel injector port configuration which can better atomize fuel injected into a combustion chamber from an accumulator at cold engine start-up, thereby resulting in better burning process. This, in turn, can eliminate the bucking behavior during startup or warm-up time.
In accordance with one aspect of the present invention, an internal combustion engine is provided having a cylinder with a piston movement area; a piston movably mounted in the cylinder; an ignition system connected to the cylinder; and a fuel delivery system connected to the cylinder. The fuel delivery system has a combined fuel and air injection port extending into the cylinder. The injection port has an end at the piston movement area with a top surface and a different shaped bottom surface. The bottom surface has an upwardly tapering shape to form a bottom portion of the end of the injection port with a generally semi-conical shape.
In accordance with another aspect of the present invention, an internal combustion engine is provided having a cylinder, a piston movably mounted in the cylinder, an ignition system connected to the cylinder, and a fuel delivery system for delivering fuel into the cylinder. The fuel delivery system includes a fuel and air injection port through the cylinder. The injection port has a substantially straight circular cross section along a majority of its length and a curved tapering surface along its bottom side at an exit from the injection port into the cylinder.
In accordance with one method of the present invention, a method of manufacturing a cylinder for an internal combustion engine is provided comprising steps of providing a cylinder member with a piston movement area; forming a channel through the cylinder member up to an inner wall of the cylinder at the piston movement area, an end of the channel proximate the inner wall having a general conical shape; and removing an upper portion of the general conical shape at the end of the channel to form an injection port exit into the piston movement area of the cylinder member.